Diode-pumped OPS lasers are now being increasingly used as an alternative to diode-pumped solid-state lasers. The most common OPS lasers employ gallium-arsenide-substrate (GaAs-substrate) based devices and provide fundamental radiation at a wavelength of about 980 nm or thereabouts. This is a preferred pump wavelength for fiber lasers. This fundamental wavelength can be frequency-doubled to provide radiation having a wavelength of about 490 nm that is useful in optical inspection apparatus and forensic lasers. The fundamental wavelength can also be frequency tripled or frequency quadrupled to provide ultraviolet radiation having wavelengths of about 327 nm or 245 nm respectively. These ultraviolet wavelengths are useful in optical inspection, machining, and optical lithography operations.
To date there has not been developed a commercial diode-pumped OPS laser capable of providing fundamental radiation at mid-IR wavelengths, for example, at wavelengths of about 1500 nm and longer. This would require development of an indium-phosphide-substrate OPS-structure. One possible reason for this is that there are no readily available diode-lasers that can be used for pumping such a structure even were one to be developed.
An alternative approach would be to frequency divide fundamental radiation of a 980 nm (or thereabouts) wavelength OPS by using the fundamental radiation to pump an OPO. By way of example, radiation having a wavelength between about 970 nm and 990 nm from a readily available, diode-pumped OPS laser could be frequency divided in an OPO to a signal portion having a wavelength between about 1321 nm and 1368 nm, and an idler portion having a wavelength between about 3585 nm and 3646 nm.
Two configurations of an OPS-pumped OPO are described in U.S. Pat. No. 5,991,318, the complete disclosure of which is hereby incorporated by reference. One configuration is a collinear configuration wherein an optically nonlinear crystal arranged for optical parametric frequency dividing is located in a common arm of a two-branch resonator formed by two mirrors and a mirror-structure of an OPS-structure. The other configuration is a non-collinear configuration including an OPS resonator and an OPO resonator having longitudinal axes intersecting in an optically nonlinear crystal arranged for optical parametric frequency dividing. It is believed that while these OPS-pumped OPO configurations can provide adequate frequency dividing, more complex configurations are required to optimize the frequency dividing process.